Wellbores are conventionally logged to determine rock and fluid properties of subterranean hydrocarbon-bearing formations traversed by the wellbore. The resulting information can be used to better manage production of hydrocarbons from the formation. U.S. Pat. No. 4,312,049 discloses a method employing acoustic logs to identify the gas, oil and water zones in a subterranean formation. Acoustic logging is typically performed in production or injection wells as disclosed in U.S. Pat. No. 4,934,186. However, such well logging activities can be disruptive to the day to day hydrocarbon production operations due to placement of the logging tool in the wellbore being logged. The present invention recognizes a need for a method of locating the contact levels of oil, gas and water zones in an oil reservoir and continuously monitoring the reservoir contact levels over an extended period of time without substantially disrupting oil production from the reservoir.
Accordingly, it is an object of the present invention to provide a method for effectively monitoring contact levels of oil, gas and water zones in an oil reservoir. It is another object of the present invention to continuously monitor the reservoir contact levels over an extended period of time. It is a further object of the present invention to monitor reservoir contact levels without substantially disrupting oil production from the reservoir. It is yet another object of the present invention to monitor reservoir contact levels over an extended period of time by means of a tool requiring little user intervention. It is still another object of the present invention to monitor reservoir contact levels at a plurality of locations in the reservoir over an extended period. It is a further object of the present invention to transmit reservoir contact levels obtained from a plurality of locations in the reservoir to a remote central management office for use by the operator. It is another object of the present invention to use the reservoir contact levels obtained from a plurality of locations to manage production of oil from the reservoir via a plurality of production wells. These objects and others are achieved in accordance with the invention described hereafter.